Webclient: change 2 topic DOM hooks (#505).

BREAKING CHANGE

View Customization Framework:

- 2 hooks don't have the `topic_dom` parameter anymore, just the `topic_view`:
    - topic_dom(topic_view)
    - topic_dom_appendix(topic_view)
  The topic DOM is available (as usual) at `topic_view.dom`

See #505.
Webclient: rename 3 view customizer hooks (#505).

BREAKING CHANGE

View Customization Framework:

- 3 hooks are renamed:
    - update_topic()           -> on_update_topic()
    - move_topic()             -> on_move_topic()
    - update_view_properties() -> on_update_view_properties()

The "on" prefix tells: "the underlying topic viewmodel has changed. Now, dear view customizer, its up to you to sync the view accordingly". Syncing the view includes:
    a) update possible viewmodel-related custom properties e.g. the topic's bounding box (in case of Canvas based rendering).
    b) update the topic DOM (in case of DOM based rendering).

See #505.
Topicmaps: fix topic update.